This application is based on an incorporates herein by reference Japanese Patent Application No. 2000-303137 filed on Oct. 3, 2000.
1. Field of the Invention
The present invention relates to a method of working an injection hole of a fuel injection nozzle plate of a fuel injection valve for injecting fuel into an internal combustion engine. The injection hole having a diverging shape with an increasingly larger diameter from a fluid inlet to a fluid outlet.
2. Description of the Related Art
Generally known in the art is an electromagnetic type fuel injection valve arranged with a thin plate having a plurality of injection holes on a downstream side of a fuel valve portion. The fuel injection valve portion further possesses a nozzle needle and a valve seat of a valve body for injecting fuel from the respective injection holes. It is conventional that the injection holes formed in a plate for fuel injection are provided with a diameter which stays the same from a fuel inlet to a fuel outlet, however, according to U.S. Pat. No. 4,907,748, there is shown a plate with an injection hole formed in a diverging shape, that is, injection holes that increase in diameter from the fuel inlet to the fuel outlet.
In recent years, there has been expedited needs for highly small particle formation of sprayed fuel in an electromagnetic type fuel injection valve and there has been requested high precision working of an injection hole formed in a orifice plate integrated to a front end face of a valve body to close an opening formed at a front end portion of the valve body. Heretofore, small particle formation of sprayed fuel in an electromagnetic type fuel injection valve has been dealt with by miniaturization and large angle formation of an injection hole.
However, as a method of working an injection hole for forming an injection hole in a diverging shape in a plate-like material, removal machining such as electric discharge machining (EDM) has been used which takes a working time period of several tens of seconds. Experience with EDM proves that the dimensional accuracy is poor as is the accuracy of a flow rate of sprayed fuel. At the same time, when the number of electric discharge machines is increased for the purpose of producing a number of parts to meet market demands, large expenses are required in plant and equipment investment resulting in increased production costs.
Hence, there is conceivable a method of extrusion using a punch for working an injection hole which is capable of resolving the above-described problem. However, when a central axis line of an injection hole is at an angle to a line perpendicular to a face of a plate-like material before working the desired injection hole, there is a possibility of breaking the punch due to the existence of a side force exerted on the punch when the front end of the punch impinges on the plate-like material (this is a force orthogonal to the central axis line of the punch). Therefore, it has been difficult to adopt extrusion methods using a punch as the method of working the injection hole.
It is an object of the invention to realize a method of working an injection hole of a fluid injection nozzle capable of reducing production costs and capable of increasing productivity. Further, it is an object to achieve dimensional accuracy of the injection hole and accuracy of a fluid flow rate which has not been achievable by removal working methods such as electric discharge machining (EMD) or press-punching. Further, it is an object to realize an apparatus of working an injection hole of a fluid injection nozzle in which even when extrusion using a punch is adopted, the punch will not break.
According to a first aspect of the invention, there is adopted an apparatus of working an injection hole of a fluid injection nozzle having a die mounted with a plate-like material, a punch substantially in the shape of a truncated circular cone, a shape of a front end portion of which is provided with a first inclination angle and a second inclination angle relative to a line perpendicular to a face of the plate-like material, a punch guide having a support hole slidably supporting the punch such that a central axis line of the punch is inclined to a perpendicular line of the face of the plate-like material, and punch driving means for advancing the punch in a direction of a central axis line of the punch guide.
Further, when a central axis line of the injection hole is inclined to a perpendicular line of the plate-like material face, by using a die structure capable of receiving a side force at a front end portion of the punch produced by working the injection hole, an inner face of the injection hole can be provided with a uniform face condition. That is, the face condition will be uniform over an entire region of the inner face of the injection hole without producing a broken face as in conventional press-punching. Therefore, a method is realized whereby working an injection hole of a fluid injection nozzle reduces production costs and improves productivity.
Further, by adopting extrusion using the punch, dimensional accuracy and accuracy in a flow rate is achievable. Accuracy and flow rates are not achievable by removal working methods such as electric discharge machining or press-punching. Further, the side force (force in a direction orthogonal to a central axis line of the punch) evident when the front end portion of the punch reaches the injection hole, can be opposed by a sliding face of the punch guide on a side opposed to the plate-like material. The side force is canceled by a reaction force, therefore a bending moment for breaking the punch is not created. Therefore, the punch is not broken by the side force produced when the front end portion of the punch reaches the injection hole.
According to a second aspect of the invention, a sliding face of the punch guide on which the front end portion of the punch slides is provided with the first inclination angle relative to the perpendicular line of the face of the plate-like material. The shape of the front end portion of the punch is constituted by a shape along the sliding face of the punch guide by inclining the front end portion of the punch guide in a direction opposed to a direction of the plate-like material relative to the central axis line of the punch. An effect (material removal effect) similar to that of the invention described in the first aspect can further be expected.
According to a third aspect of the invention, in working (forming) the injection hole, in a state in which the plate-like material is held between the die and the punch guide, there is carried out extrusion by pressing the front end portion of the punch into the plate-like material by advancing the punch along the central axis line of the punch guide in the direction of the plate and extruding a volumetric portion which the front end portion of the punch contacts as the punch progresses. The shape of the front end portion of the punch penetrates the plate-like material to thereby form the injection hole having the desired punch shape. An effect similar to that of the invention described in the first aspect can be expected to a further degree.
According to a fourth aspect of the invention, there are provided press dies setting a clearance between the front end portion of the punch and the die in a predetermined range relative to a plate thickness of the plate-like material. Further, the plate-like material is formed with the desired shape of the injection hole by executing a step of removing an extruded volumetric portion, which the front end portion of the punch presses and expels after the extrusion, by cutting, machining, or grinding the extruded portion at a level consistent with the face of the plate-like material.
According to a fifth aspect of the invention, there are provided press dies setting a clearance between the front end portion of the punch and the die to be equal to or smaller than a predetermined value. Further, the desired shape of the injection hole is formed in the plate-like material by pressing the punch until the extruded volumetric portion, which the front end portion of the punch presses to exclude, is separated from the plate-like material in the extrusion. The removing step is abolished and therefore, production costs are reduced.